The present invention relates to a control device for an optical amplifier included in an optical communication system and, more particularly, to an optical amplifier control device capable of reducing the output power of the amplifier in a predetermined situation, e.g., when an output connector comes off.
In an optical communication system, an optical transmitter emits a high-output optical signal. This kind of optical signal is harmful to the eye of a person performing maintenance or inspection. A control device for an optical amplifier is conventional which detects the come-off of an output connector included in the amplifier or similar accident in response to the resulting increase in the reflection of the optical signal and automatically reduces the output power of the amplifier. When, for example, the output connector is fixed again, the control circuit automatically restores the output power on detecting the resulting decrease in reflection. General optical output control for an optical communication apparatus is taught in Japanese Utility Model Laid-Open Publication No. 63-64142. Implementations relating to optical transmission are also disclosed in Japanese Patent Laid-Open Publication Nos. 58-86786 and 60-72429 and Japanese Utility Model Laid-Open Publication No. 62-158408 by way of example.
Assume that an optical amplifier outputs power Po, and that light reflected from the end face of an output connector and a transmission path to which the connector is connected has power Pr. It has been customary with a control device of the type controlling the output of an optical amplifier to monitor a ratio Pr/Po, reduces the output power when the ratio Pr/Po exceeds a preselected threshold, and restores the output power when it decreases to below the threshold. However, the problem with the conventional control device is that it is complicated and bulky since it needs relatively large scale circuitry.